Laminated glazings are currently in very widespread use in building, transport, optical instrument industries, etc. These laminates are generally formed from several sheets of glass and/or rigid plastic materials in which intercallated sheets are adhered, for example, sheets of polyvinylbutyral. Recently, laminated glazings have appeared comprising, in addition to the elements already described, a sheet of plastic material that possesses good antilaceration and self-healing properties. In automotive glazings of this type, for example, automobile windshields, the antilacerative material is oriented toward the interior of the vehicle so as to protect the occupants of the vehicle from contact with broken glass should the windshield be broken accidentally.
It is important, especially for safety reasons, that automobile windshields have good optical qualities and that they be free of distortions. Thus, particular care must be exercised during their manufacture to avoid defects that can result when particles are present between the self-healing layer and the underlying glass; such particles create optical defects in the form of distortions and/or lenses.
When the sheet of plastic material that is laminated to the glass is polyvinylbutyral or, more generally, a thermoplastic material, the fine specks of dust that might be on the surface of the sheet are not visible because they are embedded in the thermoplastic layer during the assembly of the laminated glass.
On the other hand, when one utilizes sheets having one side formed from a thermoset material, as is the case in the safety window previously mentioned, the grains of dust or other particles are not embedded in the thermoset material when the window is assembled and can provoke the optical defects previously mentioned. Even when the sheet of plastic material has one side formed of a thermoplastic layer, particles do not become completely embedded because the thermoplastic layer is very thin.
It is therefore very important that the sheets of plastic material utilized in the manufacture of a laminated glazing be perfectly clean and free of particles, particularly when the sheet is of one of the types noted above.
It has already been proposed to clean sheets of plastic material by utilizing an apparatus combining the actions of a brush with soft bristles, suction nozzles and antistatic elements that remove the electrical charge on the sheet in the cleaning area. The removal of electrical charge is essential to avoid the deposit of dust or other particles, during the cleaning operation, on the sheet of plastic material, which is generally very susceptible to static electrical charge phenomena.
Such an apparatus is not entirely satisfactory because, in particular, very small particles can pass between the brush bristles. Such apparatus is even less effective for cleaning a sheet that includes a layer that has an adhesive tack. In this latter instance, virtually none of the particles adhered to the tacky layer are eliminated.